1. Field of the Invention
The invention relates generally to navigation and more specifically to equipment and methods for finding one's position on a map with the aid of a global positioning system receiver.
2. Description of the Prior Art
Global positioning system (GPS) receivers conventionally output position indications in terms of longitude and latitude. Relating that information to a road map, atlas or topographic map has been difficult for lay people, and errors in understanding one's real position relative to a map are frequently made. For example, the United States Geological Survey (USGS) (Denver, Colo.), publishes 7.5 minute series topographical maps that divide the Continental United States into 53,000 quadrangles of 7.5 minutes longitude and 7.5 minutes latitude. Boulder Creek, Calif., is represented on the topographical map uniquely titled, "Castle Rock Ridge Quadrangle, California". The southeast corner of this particular USGS map is identified as being 37.degree.07'30" north latitude and 122.degree.00' west longitude. The northwest corner is also identified, as being 37.degree.15' north latitude and 122.degree.07'30" west longitude. Boulder Creek, Calif., lies at the southwest corner, identified as being 37.degree.07'30" north latitude and 122.degree.07'30" west longitude. Saratoga, Calif. lies near the northeast corner, which is identified as being 37.degree.15' north latitude and 122.degree.00' west longitude. These maps further show 2'30" divisions of latitude and longitude, which divide each quadrangle map sheet into nine parts, a matrix three-by-three. The map scale is 1:24,000, meaning one inch represents 24,000 inches on land, or 2,000 feet.
It is possible therefore, to manually figure out which spot on a particular USGS map represents a users position as originally determined in terms of latitude and longitude from a conventional GPS receiver display.
A conventional GPS receiver with the ability to communicate the desired heading to a user is described by Isaac N. Duraboraw, III, in U.S. Pat. No. 5,266,958, issued Nov. 30, 1993, which is incorporated herein by reference. A simple indication of the direction of the desired heading is indicated during the user's swinging of the GPS receiver in a horizontal circle. A visual or audible alert tells the user which part of the circle lies in the direction of the desired heading.
The GPS is a satellite-based radio-navigation system from which extremely accurate time and navigational information can be computed. A user's three-dimensional position and velocity can be computed for any point on or near earth. The GPS several satellites evenly dispersed in three, inclined, 12-hour circular orbits chosen to insure continuous 24-hour coverage worldwide. Each satellite carries extremely accurate cesium and rubidium vapor atomic clocks providing timing information. Additionally, each satellite is provided with clock correction and orbital information by earth-based monitoring stations.
Topographical map users need a quick and easy method to determine and record their precise position on any topographical (TOPO) series map. Such maps have a datum located somewhere on the map itself, such as at a bottom right corner, e.g., the south east corner, that provides the latitude and longitude at that point. The map further provides a scale factor that can be used to convert, for example, inches on the map to miles over the terrain. Users could benefit from a system that could provide position information in any one of several different formats, starting from four inputs consisting of a datum input, a scale factor, and the horizontal and vertical distances on the map from the datum. A GPS receiver that provided current position information from a user selected reference point, such as the south-east datum of a map page, would be useful if inches "over and up" from the datum were displayed on the GPS receiver's screen.
Besides the longitude-latitude format, other formats for position identification include universal transverse mercader (UTM), Maidenhead, TRIMBLE GRID LOCATOR.TM., OSGB and Thomas Brothers.TM. Maps. Maidenhead is a system used by the world's amateur radio operators to describe locations in alternating sequences of two letters followed by two digit numbers. Each pair adds precision to the position description, and Maidenhead coordinates can be readily communicated over radio channels, even when the reception is poor. TRIMBLE GRID LOCATOR (TGL) is a proprietary map coordinate system marketed by Trimble Navigation (Sunnyvale, Calif.) for use with GPS receivers. The TRIMBLE ATLAS is based upon the North American Datum, 1983 (NAD 83).
A regional map of the United States is provided in atlas form for the TGL system and provides a regional map scale of one inch to thirty miles and an area map scale of one inch to five miles. Table I lists the nine regions of the United States.
TABLE I ______________________________________ Region 1: Pacific Northwest Region 2: Mountain Region 3: North Central Region 4: Great Lakes Region 5: Northeast Region 6: Pacific Southwest Region 7: Four Corners Region 8: South Central Region 9: Southeast ______________________________________
Area pages following each regional section provide close-up views of selected metropolitan areas, and show an entire street network. For example, San Jose, Calif., is shown on a page identified "R6 263" for region six, area page 263. On that page in the atlas, grid coordinates are provided A-L left to right, and 1-11 top to bottom. The San Jose International Airport (SJC) can be seen as being located in grid J5, area page 263, R6. This could alternatively be expressed as "R6,263,J5".
Each page and grid location can be sub-divided into nine equal sub-grids, such as in Table II. This allows for greater resolution in pinpointing a given location. In the example, SJC is located in sub-grid "UR", making it, "R6,263,J5,UR".
TABLE II ______________________________________ UL UC UR ML MC MR LL LC LR ______________________________________
The abbreviations used for the nine equal sub-grids are expanded in Table III.
TABLE III ______________________________________ UL Upper Left UC Upper Center UR Upper Right ML Middle Left MC Middle Center MR Middle Right LL Lower Left LC Lower Center LR Lower Right ______________________________________
Given the prior art, it would be difficult to find one's position using such an atlas, given only longitude-latitude information, such as is provided by a conventional GPS receiver. A GPS receiver that would display TGL information directly for a user's position would be more useful.
GPS receivers conventionally provide for input of a series of waypoints on a path to a goal destination. Off-track information is typically provided real time to inform a user how far off, left or right, the actual track is off from the ideal track. Such information is not very useful to hikers who are more concerned with what their heading should be, with regard to where they are presently. A target tracking display on a GPS receiver is needed to show users their current position, relative to their goal destination. A distance and speed indication would also be useful.